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© 1999 International Anesthesia Research Society
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Abstract |
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Bilateral breath sounds are routinely auscultated after endotracheal intubation to verify that the endotracheal tube (ETT) tip is properly positioned. We conducted the present study to ascertain whether the eye of the Murphy tube has an influence on the reliability of auscultation of breath sounds in detecting endobronchial intubation. Twenty patients undergoing scheduled oral and maxillofacial surgery participated in this study. After the induction of general anesthesia, either the Magill tube or the Murphy tube was inserted through the nose into the trachea. The fiberoptic bronchoscope was inserted through the ETT, and the distance from the nares to the carina of the trachea was measured. When breath sounds from the left side of the chest changed and disappeared while the ETT was being advanced, the distance from the nares to the ETT tip was measured. Unilateral auscultatory change was not observed until the ETT tip was advanced beyond the carina and inserted 1.5 ± 0.4 cm into the right mainstem bronchus when the Magill tube was used and 2.0 ± 0.4 cm when the Murphy tube was used (P < 0.01). Breath sounds disappeared when the ETT tip was further advanced up to 3.2 ± 0.3 cm from the carina. We demonstrated that the eye of the Murphy tube reduces the reliability of chest auscultation in detecting endobronchial intubation.
Implications: The Murphy eye was designed to allow ventilation of the lung when the bevel of the endotracheal tube is occluded. We demonstrated that the eye of the Murphy tube reduces the reliability of chest auscultation in detecting endobronchial intubation.
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Introduction |
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Inadvertent endobronchial placement of the endotracheal tube (ETT) during general anesthesia can lead to serious complications, such as atelectasis, hypoxemia, pneumothorax, cardiac arrhythmia, and hypotension (1,2). To prevent these intraoperative complications, criteria including auscultation of bilateral breath sounds, observation of symmetric chest expansion, palpation of the ETT cuff in the suprasternal notch, use of the centimeter markings printed on the ETT, and postintubation chest radiographs have been clinically adopted (2–5). Particularly, chest auscultation has been widely used for determining the proper position of the ETT after endotracheal intubation in the operating room or the emergency unit (1,6). However, investigations have revealed that auscultation is a poor diagnostic modality for endobronchial intubation. Brunel et al. (1) noted that 60% of mainstem endobronchial intubations occurred despite the presence of equal breath sounds on auscultation. The results of our previous study suggested that the inaccuracy of the auscultation method was related to the structure of the tip of the ETT inserted into the trachea (7). The tip of the tracheal end of the ETT is commonly beveled. The ETT with a simple beveled tip is called the Magill tube. The ETT with an oval hole on the side opposite to the bevel, which is known as the Murphy eye, is called the Murphy tube. In the present study, we attempted to ascertain whether the eye of the Murphy tube is related to the unreliability of auscultation of breath sounds in detecting endobronchial intubation.
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Methods |
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The study protocol was approved by the institutional review board of our hospital. Twenty ASA physical status I Japanese women scheduled to undergo elective oral and maxillofacial surgery under general anesthesia participated in this study after providing written informed consent. Patients with pulmonary diseases such as bronchial asthma, abnormal breath sounds, and malformations of trachea, bronchus, and lung in chest radiographs were excluded from the study.
Premedication consisted of 0.5 mg of scopolamine and 15 mg of pentazocine administered IM 30 min before the patients were taken to the operating room. Anesthesia was induced with 4–5 mg/kg thiopental IV, and nasotracheal intubation was facilitated with the IV administration of 0.1 mg/kg vecuronium. Either a Portex Blue Line Tracheal TubeTM (Magill tube group) or a Portex Clear Tracheal Tube Murphy EyeTM (Murphy tube group), with an inner diameter of 7.5 mm (Portex Limited, Hythe Kent, UK), was inserted after it was lubricated with lidocaine spray. The tube was selected for a given patient in a randomized fashion. Oxygen, nitrous oxide, and isoflurane (1.0%–1.5%) were administered. After the cuff of the ETT was inflated (cuff pressure 20 cm H2O) and the patient's head was placed in a neutral position, the fiberoptic bronchoscope (FOB) was inserted through the ETT. Both the FOB and the ETT with the inflated cuff were gently advanced. When it was confirmed with the FOB that the tip of the ETT had reached the carina of the trachea, a mark was made on the ETT at the nares. After the FOB was removed, the ETT was withdrawn several centimeters, then advanced again while auscultating bilateral breath sounds with a stethoscope placed on the midaxillary line at the level of the fourth intercostal space during manual compression of the reservoir bag (airway pressure 15–20 cm H2O, tidal volume 400–450 mL). When breath sounds from the left side of the chest first changed in quality (rough, bubbling, wheezing, or bronchial) and disappeared completely, a second and third mark were made on the ETT at the nares. This made it possible to measure the distance from the nares to the carina and the distances from the nares to the ETT tip at the change and disappearance of breath sounds. Using these values, the distances from the carina to the ETT tip at the change and disappearance of breath sounds were calculated. The anesthesiologist who ausculted breath sounds, and who had extensive experience in practicing general anesthesia (>20 yr), was different from the individual who inserted the ETT into the trachea and was thus blinded to the type of ETT used. Patients in whom the insertion of the ETT into the left mainstem bronchus was verified by the FOB were excluded from the study. The distance from the tip of the ETT to the distal end of cuff was measured in all tubes used in this study.
Values are expressed as mean ± SD. Variables in the same group were analyzed by using a paired Student's t-test, and comparisons between the Magill tube group and the Murphy tube group were conducted using an unpaired Student's t-test. A P value of <0.05 was considered significant.
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Results |
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There were no significant differences between the Magill tube and Murphy tube groups regarding age, weight, or height (Table 1).
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Both the Magill tube and the Murphy tube have a cuff made of polyvinyl chloride 2.5 cm from the tip and a 1.0-cm bevel facing to the left. The Murphy tube only has a 1.0-cm elliptical port located 0.8 cm from the tip in the wall opposite the bevel (Fig. 1).
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Fiberoptic bronchoscopy showed that the carina of the trachea was 28.7 ± 1.2 and 28.8 ± 1.6 cm from the nares in the Magill tube and Murphy tube groups, respectively. When breath sounds from the left side of the chest changed in quality and disappeared, the ETT tip was located 30.1 ± 1.3 and 31.9. ± 1.0 cm from the nares in the Magill tube group and 30.8 ± 1.7 and 31.9 ± 1.7 cm from the nares in the Murphy tube group. The distances from the nares to the ETT tip at the change and at the disappearance of breath sounds were significantly longer than the distance from the nares to the carina in both groups (P < 0.01) (Table 2).
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Unilateral auscultatory change was not observed until the ETT tip was advanced beyond the carina and inserted 1.5 ± 0.4 and 2.0 ± 0.4 cm into the right mainstem bronchus in the Magill tube and Murphy tube groups, respectively. These two values were significantly different (P < 0.01). Breath sounds disappeared when the ETT tip was further advanced up to 3.2 ± 0.3 cm from the carina in both groups (Table 3).
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Discussion |
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After tracheal intubation for general anesthesia, proper positioning of the ETT tip has been routinely verified by using chest auscultation of breath sounds. Schwartz (6) has emphasized the importance of bilateral breath sounds as a tool to detect intraoperative complications, such as endobronchial intubation and obstructed airway, and recommended continuous auscultation using a precordial stethoscope. In fact, the unilateral change and disappearance of breath sounds requires withdrawing the ETT until bilateral breath sounds become equal in quality and loudness. This maneuver is based on the premise that equal breath sounds from the bilateral chest indicate that the ETT tip is placed above the carina of the trachea. In the present study, bilateral breath sounds were equally audible even when the ETT tip was advanced beyond the carina. Breath sounds from the left side of the chest did not change and did not disappear until the tip entered the right mainstem bronchus, approximately 1.5 and 3.2 cm for the Magill tube, and 2.0 and 3.2 cm for the Murphy tube, respectively. These results show that the above-mentioned premise was not true of the patients in our study, which implies the unreliability of the auscultation of bilateral breath sounds for confirming proper placement of the ETT. However, the clinical application of our data could enhance the value of the auscultation method to some degree. The present findings reveal that, when the breath sounds changed, the ETT tip was located an average of 1.5 and 2.0 cm beyond the carina in the right mainstem bronchus in the Magill tube and Murphy tube groups, respectively. This means that at the change of breath sounds, withdrawal of the ETT by >1.5 cm for the Magill tube and 2.0 cm for the Murphy tube is necessary to place the ETT tip above the carina in the trachea. Conrardy et al. (8) demonstrated that the ETT moved downward a mean distance of 1.9 cm with neck flexion from a neutral position. Based on the findings of Conrardy et al. (8) and our data, we recommend that the Magill and Murphy tubes be withdrawn approximately 3.4 and 3.9 cm, respectively, before being secured with sticking plaster if breath sounds first change while the ETT is being advanced after endotracheal intubation. This recommendation can prevent the insertion of the ETT tip into the right mainstem bronchus caused by flexion of the neck.
In previous studies, we demonstrated that breath sounds changed because the gas flow through the space between the ETT cuff and the bronchus decreased, that the breath sounds disappeared because the inflated cuff completely sealed the intubated bronchus, and that the gas flow to the opposite bronchus was interrupted (9,10). In the present study, the distance from the carina to the ETT tip at the change of breath sounds was significantly longer in the Murphy tube group than in the Magill tube group: 2.0 and 1.5 cm, respectively. This is probably due to the structural characteristics of the ETTs used in these groups. The only difference in the structure is that the Murphy tube has a hole cut in the side of the wall opposite the bevel side near the tip (the Murphy eye). The eye was originally designed to allow ventilation of the lung if the bevel is occluded with mucus and ventilation of the right upper lobe if the ETT tip is accidentally advanced into the right mainstem bronchus (11). The results of the present study show that the Murphy eye can maintain the gas flow through the space between the ETT cuff and the bronchus and that it allowed ventilation of the left lung until the ETT tip was inserted 2 cm beyond the carina, although the Murphy eye is located on the right side of the ETT. However, adequate ventilation of the left lung via the Murphy eye cannot be expected (12) when the tip is located in the right mainstem bronchus. Thus, the tip of the ETT should be kept above the carina of the trachea during general anesthesia, even when the Murphy tube is used. Based our findings that bilaterally equal breath sounds were audible with the use of the Murphy tube until the tip was inserted 2 cm into the right mainstem bronchus, we believe that the auscultation method is not very reliable for determining the proper position of the Murphy tube. Black and Mackersie (12) reported that there was a high incidence of endobronchial intubation in the oral RAE (Ring, Adair, Elwyn) tube. Because the RAE tube is bilaterally provided with two eyes near the bevel, we speculate that the eyes of the RAE tube would make it difficult to detect the endobronchial placement of the tip of the tube with auscultation. Accordingly, special attention must be given to verify proper positioning of the RAE tube with the change in breath sounds.
In the present study, the distance from the carina to the ETT tip at the disappearance of breath sounds was not significantly different between the Murphy tube and Magill tube groups. When the ETT tip was advanced a mean of 3.2 cm into the right mainstem bronchus in both groups, the breath sounds disappeared. At that time, the distal end of the cuff, which was 2.5 cm from the tip, was located 0.7 cm below the carina. This suggests that the inflated cuff was wedged into the right mainstem bronchus and interrupted the gas supply to the opposite bronchus, resulting in no ventilation of the left lung. Thus, the interruption of gas flow was observed independently of the Murphy eye. Based on this finding, we believe that the Murphy eye never plays an important role in the disappearance of breath sounds.
In conclusion, the results of the present study show that normal breath sounds could be heard from the left side of the chest until the ETT tip was advanced beyond the carina and inserted into the right mainstem bronchus more deeply with the Murphy tube than with the Magill tube. The eye of the Murphy tube reduces the reliability of chest auscultation in detecting endobronchial intubation.
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References |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Brunel W, Coleman DL, Schwartz DE, et al. Assessment of routine chest roentgenograms and the physical examination to confirm endotracheal tube position. Chest 1989;96:1043–5.
[Abstract/Free Full Text] - Schwartz DE, Lieberman JA, Cohen NH. Women are at greater risk than men for malpositioning of the endotracheal tube after emergent intubation. Crit Care Med 1994;22:1127–31.[Web of Science][Medline]
- Pollard RJ, Lobato EB. Endotracheal tube location verified reliably by cuff palpation. Anesth Analg 1995;81:135–8.[Abstract]
- Owen RL, Cheney FW. Endobronchial intubation: a preventable complication. Anesthesiology 1987;67:255–7.[Web of Science][Medline]
- Grey P, Sullivan G, Ostryzniuk P, et al. Value of postprocedural chest radiographs in the adult intensive care unit. Crit Care Med 1992;20:1513–8.[Web of Science][Medline]
- Schwartz N. Monitoring bilateral breath sound. Anesthesiology 1987;66:711–2.[Medline]
- Sugiyama K, Satoh Y, Yokoyama K. Study of changes in bilateral breath sounds with changes in position of the endotracheal tube tip. J Jpn Dent Soc Anesthesiol 1996;24:805–8.
- Conrardy PA, Goodman LR, Lainge F, et al. Alteration of endo-tracheal tube position. Crit Care Med 1976;4:8–12.
- Sugiyama K, Yokoyama K. Reliability of auscultation of bi-lateral breath sounds in confirming endotracheal tube position. Anesthesiology 1995;83:1373.
- Kubota Y, Toyoda Y, Kubota H, et al. Confirmation of endo-tracheal tube positioning. Chest 1990;98:1306.[Medline]
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Ring WH, Adair JC, Elwyn RA. A new pediatric endotracheal tube. Anesth Analg 1975;54:273–4.
[Free Full Text] - Black AE, Mackersie AM. Accidental bronchial intubation with RAE tubes. Anaesthesia 1991;46:42–3.[Web of Science][Medline]
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